Accelerated medial calcification is a major cause of premature cardiovascular mortality in people with chronic kidney disease. Evidence suggests that the concentration of extracellular Ca2+ and vascular smooth muscle cells play a pivotal role in the pathogenesis of vascular calcification. Extracellular Ca2+ is detected by the calcium-sensing receptor (CaSR). The CaSR is a G protein-coupled receptor that is expressed in a range of tissues, but characterization of the expression and function of the CaSR in the cardiovascular system is limited. Here we report the expression of CaSR mRNA and protein (Western blotting and immunocytochemistry) in human aortic smooth muscle cells (HAoSMC) and human arteries (ethical approval obtained). Incubation of HAoSMC with Ca2+(05 mM; 030 minutes) or the CaSR agonists, gentamicin and neomycin (0300 μM; 030 minutes), resulted in a dose and time dependent phosphorylation of ERK1,2. Ca2+ stimulation was maximum at 5 minutes and 3 mM (508±66% of control) (P<0.001, n=3). Stimulation with gentamicin or neomycin (10 μM; 10 minutes) caused a significant increase in ERK1,2 phosphorylation (gentamicin 241±17% of control, P<0.001, n=3; neomycin 311±13% of control, P<0.01, n=3). Gentamicin and neomycin, but not Ca2+, mediated ERK1,2 stimulation was inhibited by pre-treatment with PD-98059 (ERK-activating kinase-1 inhibitor) (P<0.01, n=3). CaSR expression in human tissues was also examined. CaSR mRNA and protein was expressed normal arteries (kidney donors) where it was detected in smooth muscle cells and endothelial cells. To investigate a functional correlation with renal disease we examined expression in arteries from patients with end stage renal disease (ESRD). Expression of the CaSR appeared to be lower in the arteries from ESRD patients and in particular it was reduced in regions of calcium deposition. Taken together these data not only demonstrate expression of a functional CaSR in human arteries, but demonstrate a correlation between CaSR expression and medial calcification.